The present invention generally relates to the use of voltage variable materials for the protection of an integrated circuit against electrical overstress (EOS) transients.
There is an increased demand for materials and electrical components which can protect electronic circuits from EOS transients which produce high electric fields and usually high peak energies capable of destroying circuits or the highly sensitive electrical components in the circuits, rendering the circuits and the components non-functional, either temporarily or permanently. The EOS transient can include transient voltage or current conditions capable of interrupting circuit operation or destroying the circuit outright. Particularly, EOS transients may arise, for example, from an electromagnetic pulse, an electrostatic discharge, lightning, or be induced by the operation of other electronic or electrical components. Such transients may rise to their maximum amplitudes in microsecond to subnanosecond time frames and may be repetitive in nature. A typical waveform of an electrical overstress transient is illustrated in FIG. 1. The peak amplitude of the electrostatic discharge (ESD) transient wave may exceed 25,000 volts with currents of more than 100 amperes.
Materials for the protection against EOS transients (EOS materials) are designed to respond essentially instantaneously (i.e., ideally before the transient wave reaches its peak) to reduce the transmitted voltage to a much lower value and clamp the voltage at the lower value for the duration of the EOS transient. EOS materials are characterized by high electrical resistance values at low or normal operating voltages and currents. In response to an EOS transient, the material switches essentially instantaneously to a low electrical resistance value. When the EOS threat has been mitigated these materials return to their high resistance value. These materials are capable of repeated switching between the high and low resistance states, allowing circuit protection against multiple EOS events. EOS materials are also capable of recovering essentially instantaneously to their original high resistance value upon termination of the EOS transient. For purposes of this application, the high resistance state will be referred to as the xe2x80x9coff-statexe2x80x9d and the low resistance state will be referred to as the xe2x80x9con-state.xe2x80x9d
FIG. 2 illustrates a typical electrical resistance versus d.c. voltage relationship for EOS materials. Circuit components including EOS materials can shunt a portion of the excessive voltage or current due to the EOS transient to ground, thus, protecting the electrical circuit and its components. The major portion of the threat transient is either dissipated at the source resistance or reflected back towards the source of the threat. The reflected wave is either attenuated by the source, radiated away, or re-directed back to the surge protection device which responds with each return pulse until the threat energy is reduced to safe levels.
A typical integrated circuit die having a plurality of input/output (I/O) conductive pads is illustrated in FIG. 3. Wires are bonded to the I/O pads and are connected to a corresponding electrical lead of a lead frame. Prior integrated circuit dies have voltage suppression components such as diodes, thyristors or transistors formed on the die near the I/O pads during the processing of the die to protect oxide layers, semiconductor junctions, and metal traces in the functional die area from the harmful effects of EOS transients. The assembly is typically encapsulated in a protective housing and the electrical leads of the lead frame which extend outwardly from the housing are formed in order to be connected to a circuit substrate (e.g., a printed circuit board). The components used to protect the functional area of the die are often relatively large, consuming costly die area which can otherwise be used for additional functions. In addition, the overall encapsulated device is relatively large, consuming costly real estate on the circuit substrate.
The present invention relates to an integrated circuit die and devices including same that include a voltage variable material to provide protection from EOS transients. Pursuant to the present invention, any voltage variable material can be used. A number of advantages are provided by the present invention, where integrated circuit devices are susceptible to high voltages associated with EOS transients.
In an embodiment, the present invention provides an integrated circuit including an electrically insulating substrate having at least one microelectronic device formed thereon. An input/output pad and a conductive member are formed on the substrate. A bond wire is electrically connected between the input/output pad and an electrical lead. A voltage variable material is located between the bond wire and the conductive member, the voltage variable material exhibits non-conductive behavior at normal circuit operating voltages and electrically connects the bond wire to the conductive member when a sufficient EOS transient is introduced into the circuit.
In an embodiment, the conductive member is a guard rail.
In an embodiment, the voltage variable material fills an entire space between the bond wire and the conductive member.
In an embodiment, the integrated circuit includes at least two input/output pads.
In yet another embodiment of the present invention, an electrical device includes an integrated circuit die, an electrical connector connected to the die, and a conductive guard rail. The electrical device also includes a voltage variable material exhibiting non-conductive behavior at normal circuit operating voltages and forming a conductive path between the electrical connector and the conductive guard rail when a sufficient EOS transient is introduced into the circuit.
In an embodiment, the electrical connector is an input/out pad.
In an embodiment, the electrical connector is a wire.
In an embodiment, the voltage variable material is selectively deposited on the guard rail, and the electrical connector is a wire juxtaposed to the guard rail.
In an embodiment, the electrical connector is a wire and the wire is coated with the voltage variable material.
In a further embodiment of the present invention, an electrical device is provided that includes a ground pad, an integrated circuit die on the ground pad, an electrical lead, and a conductive island. The conductive island has first and second electrical connectors, the first electrical connector is connected to the integrated circuit die and the second electrical connector is connected to the electrical lead. A voltage variable material is disposed between the ground pad and the island.
In an embodiment, the voltage variable material completely fills the space between the ground pad and the island.
In an embodiment, the electrical device includes a plurality of circuits.
In an embodiment, the voltage variable material is disposed between the island and the electrical lead.
In another embodiment of the present invention, an integrated circuit is provided that includes a printed circuit board having an input/output pad and a substrate having an upper surface facing toward the printed circuit board. An input/output pad is located on the upper surface of the substrate and is electrically connected to the input/output pad of the printed circuit board. A ground pad is also located on the upper surface of the substrate. A voltage variable material is located between the ground pad and the input/output pad of the upper surface.
In an embodiment, the ground pad is located in juxtaposition to the input/output pad.
In an embodiment, the voltage variable material fills the entire space between the ground pad and the input/output pad.
In an embodiment, the printed circuit board further includes a ground pad adjacent the input/output pad of the printed circuit board, and the voltage variable material electrically connects the input/output pad of the printed circuit board to the ground pad of the printed circuit board in response to an EOS transient energy.
In an embodiment, the voltage variable material fills an entire space between the input/output pad and the ground pad of the printed circuit board.
In yet a further embodiment of the present invention, an integrated circuit is provided that includes an integrated circuit die, an insulating layer on the integrated circuit die, and a first electrical connector. A second electrical connector is connected to the first electrical connector and connected to the integrated circuit die. A conductive member is located between a portion of the insulating layer and the integrated circuit die. A voltage variable material is interposed between the portion of the insulating layer and the integrated circuit die, the voltage variable material electrically connecting the second electrical connector to the conductive member when an EOS transient is introduced into the circuit.
In an embodiment, the conductive member is on the die.
In an embodiment, the conductive member is on the insulating layer.
In an embodiment, the insulating layer further includes a first side and the conductive member is located on the first side.
In an embodiment, the conductive member is a ground rail.
In an embodiment, the conductive member is a power rail.
Additional features and advantages of the present invention are described in, and will be apparent from, the detailed description of the presently preferred embodiments set forth below and the figures.